Hyperoxia is when the oxygen partial pressure exceeds 1.6 (recreational diving limit) and/or when you are exposed to elevated partial pressures of oxygen over an extended time. This exposure may lead to any number of the following symptoms:
- Visual disturbance
- Ringing in the ears
- Muscle twitching
The symptoms may be sudden or gradual. Generally, open circuit air divers will be unlikely to experience this. Your depth limits and your No Decompression Limit (NDL) will not allow you to build up a partial pressure of oxygen that could be harmful.
With 21% oxygen in your normal air mix, you would need to descend to around 8 atmospheres (ata) of pressure to take you over the partial pressure of oxygen limit. (21% = 0.21 ata partial pressure of oxygen at the surface)
- The following demonstrates the effects of depth on oxygen pressure.
- For 40 meters/130 feet dive, you are now at 5 ata of pressure: 5 × 0.21 = 1.05 ata.
- For 60 meters/200 feet, you are now at 7 ata of pressure: 7 × 0.21 = 1.47 ata.
- These examples are way over our limit of 20 meters/66 feet for this program but illustrate how the oxygen pressure increases with depth and how we can stay safe by not exceeding these limits. Your maximum depth for training will be 18 meters/60 feet and maximum recommended depth. Once you are certified, the maximum depth will be 20 meters/66 feet and the maximum recreational depth limit is 40 meters/130 feet once you receive the appropriate training and experience.
It is, however, possible with divers who use higher concentrations of oxygen in their breathing gas known as nitrox diving to come closer to oxygen toxicity. Specialized training is required for nitrox diving.
IMPORTANT: The oxygen partial pressure limit of 1.6 is reached or even passed if uncontrolled descents are not stopped.